1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a method of producing a phthalocyanine crystal, a method of producing an electrophotographic photosensitive member, a process cartridge, an electrophotographic apparatus, and a phthalocyanine crystal.
2. Description of the Related Art
An oscillation wavelength of semiconductor laser, which has been frequently used as an image exposing unit for an electrophotographic apparatus is, at present, a long wavelength such as 650 to 820 nm. Accordingly, development of an electrophotographic photosensitive member having high sensitivity to light having such a long wavelength has been advanced.
A phthalocyanine pigment is effective as a charge-generating substance having high sensitivity to light having a wavelength in such a long-wavelength region. In particular, oxytitanium phthalocyanine and gallium phthalocyanine have excellent sensitivity characteristics, and various crystal forms thereof have been reported heretofore.
An electrophotographic photosensitive member using the phthalocyanine pigment has an excellent sensitivity characteristic. However, a produced photocarrier is liable to remain on the photosensitive layer of the electrophotographic photosensitive member. Accordingly, the electrophotographic photosensitive member involves the following problem. That is, a short-term electric potential variation as a kind of memory occurs, which is liable to cause an image defect such as a ghost image, and to cause a long-term electric potential variation in association with repeated use.
Japanese Patent Application Laid-Open No. 2001-40237 reports that addition of a specific organic electron acceptor at the time of an acid pasting process for the phthalocyanine pigment exerts a sensitizing effect. However, the approach involves the following concern and problem. The additive may chemically change, thereby being difficult to transform the additive into a desired crystal form.
In addition, Japanese Patent Application Laid-Open No. 2006-72304 reports the following. When the pigment and a specific organic electron acceptor are subjected to a wet pulverization treatment, the organic electron acceptor is incorporated in a surface of the crystal simultaneously with crystal transformation, and hence the electrophotographic characteristics are improved.
However, a phthalocyanine crystal obtained by the approach does not contain the organic electron acceptor in itself, and the acceptor is merely in a state of being mixed with the crystal or merely adheres to its surface. Accordingly, the approach is identical in constitution and effect to the so-called addition at the time of dispersion in which a specific organic electron acceptor is added at the time of production of a coating liquid for a charge-generating layer.
In addition, Japanese Patent Application Laid-Open No. 2007-138153 discloses that a fluorinated aromatic compound is incorporated in a phthalocyanine crystal and Japanese Patent Application Laid-Open No. 2007-332052 discloses that an amino compound is incorporated in a phthalocyanine crystal.
As described above, various improvements have been attempted for an electrophotographic photosensitive member.
However, the alleviation of an image density variation due to an electric potential variation in the photosensitive member under various environments has been desired in association with an additional improvement in image quality in recent years. Investigations conducted by the inventors of the present invention have shown that the technology described in each of Japanese Patent Application Laid-Open Nos. 2001-40237, 2006-72304, 2007-138153, and 2007-332052 has been susceptible to improvement in terms of the suppression of an electric potential variation at the time of repeated use of an electrophotographic photosensitive member under a low-temperature, low-humidity environment.